Multi-directional steerable catheter

ABSTRACT

A bi-directional steerable catheter adapted for delivery into a patient&#39;s vasculature. The pull wires which are used to tension the deflectable segment of the steerable catheter are wound in parallel around the axis of the steerable catheter on opposite sides of the steerable catheter.

This application is a continuation of U.S. application Ser. No.14/887,203 filed Oct. 19, 2015, which is pending.

FIELD OF THE INVENTIONS

The inventions described below relate to the field of steerable guidecatheters, sheaths and introducers.

BACKGROUND OF THE INVENTIONS

Steerable catheters, including steerable guide catheters, guide sheathsand introducer sheaths, are used to gain access to the desired targetlocation within the vasculature of a patient and provide a safe, smoothconduit to guide and support another device, such as an interventionalcatheter, to a target location in the vasculature of a patient. Theinterventional catheter is typically a delivery device that carries animplant for deposit in the vasculature, or an active device that carriesout the diagnosis, therapy or intervention. Guide catheters, guidesheaths and introducer sheaths can also be used to pass fluids forvisualization, diagnosis or treatment. Provision of steering mechanismsin these catheters facilitates their navigation through the vasculatureof a patient, to gain access a target site.

SUMMARY

The steerable catheters described below provide for easy, atraumaticaccess to areas of the vasculature that are otherwise difficult toaccess, while minimizing the propensity of pull-wire operated steerablecatheters to whip, or rapidly snap from one configuration to another, asthe pull wire is tensioned to steer the device. The steerable cathetersdescribed below are constructed with components that are selected toprovide optimal stability to prevent whipping. The steerable catheterincludes two or more pull wires which are wound along a portion of thesteerable catheter, around the long axis of the steerable catheter, inparallel and circumferentially on opposite sides of the steerablecatheter, to balance the off-axis forces applied by the pull wires, andthus prevent whipping and avoiding changes in curve geometry achieved bymanipulation of the pull wires when the steerable catheter is deployedwithin the vasculature such that the wound portion of the steerablecatheter runs through a bend in the vasculature. The curve in thevasculature may be any tortuosity such as the aortic arch, the iliacbifurcation, the atrial septum, the brachial artery inlet from theaorta, etc. The deflection segment curve geometry remains more stablewhen the steerable catheter is rotated around its long axis. Theminimization of whipping is very effective, and the deflection segmentcurve geometry remains more stable, where the steerable cathetercomponents are arranged along the length of the steerable catheter suchthat the wound segments coincide with the expected bend in thevasculature in the vasculature in which it is deployed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the steerable catheter.

FIGS. 2 and 2A are schematic views of the steerable catheter with woundpull wires.

FIG. 3 is a perspective view of the steerable catheter and the woundpull wires.

FIG. 4 is a cross section of the steerable catheter of FIG. 1.

FIGS. 5 and 6 illustrate the control handle of the deflectable steerablecatheter of FIG. 1.

FIG. 7, which illustrate the steerable catheter disposed within thevasculature of a patient

DETAILED DESCRIPTION OF THE INVENTIONS

FIG. 1 illustrates the deflectable steerable catheter. The steerablecatheter 1 comprises a steerable catheter tube 2 with a catheter handle3 mounted on the proximal end 4 of the steerable catheter tube and adeflectable segment at the distal end 5, and a lumen extending throughthe tube. The steerable catheter tube includes the first, deflectablesegment 2 d which is operated by a pull wire, a second, wound segment 2w (extending proximally from the first segment) in which the pull wiresare wound around the catheter (shown in FIGS. 2 through 4), and,optionally, a third, proximal segment 2 p (extending proximally from thesecond segment), in which the pull wire runs straight on opposite sidesof the steerable catheter tube. The catheter handle includes a steeringlever 6, which can be turned by a user to manipulate an internalsteering mechanism (show in FIGS. 5 and 6) and the pull wires, and thusdeflect the deflectable segment in to an arcuate configuration, and abrake 7 which can be manipulated to lock the steering mechanism in anyselected position and thus hold the deflectable segment in an arcuateconfiguration selected by the user of the device, and corresponding tothe rotational position of the steering lever. As shown in phantom, thedeflectable segment 2 d is operable, through manipulation of thesteering lever, to bend through a significant arc, away from thelongitudinal axis 8, in two directions in the same plane (where two pullwires are provided), so that the tip can be deflected through an arcintersected by the longitudinal axis, without the need to rotate thesteerable catheter about the longitudinal axis. This behavior isreferred to bi-directional steering.

FIGS. 2 and 3 illustrate the steerable catheter and wound pull wiresembedded within the catheter wall and arranged to provide steeringwithout whipping. The major components of steerable catheter tube 2include the catheter wall 9 comprising an outer tube or jacket 10 and aninner tube 11, and two pull wires 12 and 13 disposed between the outertube and the inner tube. In the wound segment of the steerable catheter(2 w in FIG. 1), the pull wires are wound about the longitudinal axis ofthe tube, and each pull wire is wound in the same direction as the otherpull wire in wound wire segments 12 w and 13 w, preferably substantiallyin parallel, to create a segment of the steerable catheter in which thepull wires are wound on circumferentially opposite sides of thesteerable catheter at each point along the length of the wound segment 2w (that is, in any radial cross section, the wound wires will be onopposite sides of the steerable catheter, though along the s of thewound segment the pull wire wrap around the steerable catheter). Eachpull wire has a straight distally extending segment 12 d and 13 d,extending from the wound segment, toward the distal end of the steerablecatheter (corresponding to the deflectable segment 2 d in FIG. 1), and astraight proximally extending segment 12 p and 13 p extending proximallyfrom the wound segment toward the proximal end of the steerable catheter(corresponding to the proximal segment 2 p in FIG. 1), where they arefixed to the control mechanism shown in FIG. 4. The straight distallyextending segments 12 d and 13 d correspond to the deflectable segment 2d of FIG. 1. The pull wires may be disposed within separate side lumens18 and 19 in the wall of the inner tube or outer tube or they may bedisposed within separate smaller tubes secured over the inner tube.

As shown in FIG. 2A, in the wound segment of the steerable catheter(item 2 w in FIG. 1), the pull wires may be counter-wound, rather thanparallel, with each pull wire wound in a direction opposite the otherpull wire in wound wire segments 12 w and 13 w, to create a segment ofthe steerable catheter in which the pull wires are counter-wound. Thecounter-wound segments of the pull wires may be wound with one pull wirewithin the other, or they may be braided.

FIG. 4 is cross section of the steerable catheter, showing additionallayers of the steerable catheter. As shown in FIG. 4, the deflectablesegment 2 d of the steerable catheter tube 2 consists of the inner tube11, and straight distally extending segments 12 d and 13 d of the pullwires (disposed on opposite side of the steerable catheter, about 180°apart, both within 0.001″ thick PTFE pull wire liners), the deflectablesegment also includes a braid 14 d (1 over 1 under, 20-30 picks perinch), over the inner tube 11 and the pull wires, all within the outertube 10. Where the inner tube comprises PTFE, no liner may be necessary,but in alternative embodiments in which the inner tube comprises anotherpolymer, the deflectable segment may consist of, in addition to thelayers just listed, a PTFE liner 15, disposed within the inner tube. Thebraid 14 d may be embedded in a low durometer polymer, in which case thedeflectable segment may consist of, in addition to the layers listedabove, the braid embedded in a low durometer polymer.

A segment 2 w proximal to the deflectable segment, in which the two pullwires are wound about the axis of the steerable catheter, consists ofthe inner tube 11, then the wound segments of the pull wires (12 w and13 w), a second braid segment 14 w (1 over 2 under, at 70-80 picks perinch), within the outer tube 10. (The second braid segment 14 w may bean continuous extension of the braid 14 d in the deflectable segment, orit may be a discrete additional component.) Again, where the inner tubecomprises PTFE, no liner may be necessary, but in alternativeembodiments in which the inner tube comprises another polymer, the woundsegment 2 w may consist of, in addition to the layers just listed, thePTFE liner 15, disposed within the inner tube. The braid 14 w may beembedded in a high durometer polymer, in which case the deflectablesegment may consist of, in addition to the layers listed above, thebraid embedded in a high durometer polymer. An additional braid 16 maybe embedded in the outer tube (this braid extends proximally to the pullwire exit at the proximal end of the tube, and is preferably wound at 80picks per inch for some applications, and 20 picks per inch for otherapplications). Where, in alternative embodiments, the additional braid16 is used, the wound segment 2 w may consist of, in addition to thelayers listed above (the inner tube 11, the pull wires 12 and 13, thebraid 14 w and the outer tube 10, or the liner 15, the inner tube 11,the pull wires 12 and 13, the braid 14 w and the outer tube 10), theadditional braid 16.

A third, proximal-most segment 2 p, in which the two pull wires runstraight along the length of the catheter, from the wound segments ofthe pull wire to connections in the handle, consists of, or comprises,the inner tube 11, the second braid 14 w (the same braid as in the woundsegment) (1 over 2 under, at 70-80 picks per inch), then the straightsegments of the pull wires (12 p and 13 p) within the outer tube 10.Again, where the inner tube comprises PTFE, no liner may be necessary,but in alternative embodiments in which the inner tube comprises anotherpolymer, the proximal segment may consist of, in addition to the layersjust listed, the PTFE liner 15, disposed within the inner tube. Thebraid 14 w may be embedded in a high durometer polymer, in which casethe deflectable segment may consist of, in addition to the layers listedabove, the braid embedded in a high durometer polymer. As in the woundsegment, the additional braid 16 may be embedded in the outer tube inthe third, proximal-most segment 2 p. Where, in alternative embodiments,the additional braid 16 is used, the wound segment 2 w may consist of,in addition to the layers listed above (the inner tube 11, the pullwires 12 and 13, the braid 14 w and the outer tube 10, or the liner 15,the inner tube 11, the pull wires 12 and 13, the braid 14 w and theouter tube 10), the additional braid 16.

A soft tip 17 covers the distal tip of the device. The hardness of theouter tube can be very soft at the distal tip at 35D, and transition toprogressively harder formulation of 55D proximate the distal end of thewound segment, and then transition further to a harder formulation ofabout 72D proximate the proximal end of the wound segment, and remain atabout 72D or harder for the remaining proximal portion of the steerablecatheter.

While the steerable catheter is illustrated with two pull wires, thebenefits of the wound pull wires can be achieved with a plurality ofpull wires obtain steerability across several planes. For example, thesteerable catheter may comprise three or four pull wires, dispersed(preferably evenly distributed) about the circumference of the steerablecatheter and wound substantially in parallel in the wound segment, toprovide steering along arcs lying in additional planes.

FIGS. 5 and 6 illustrates the catheter handle of the deflectablesteerable catheter of FIG. 1, with a braking system that can be usedwith the pull wire system of FIGS. 1 through 4. The catheter handle 3 isfixed to the steerable catheter tube 2. The inner tube 11 of thecatheter extends through the catheter handle to the feeder tube 21, sothat working catheters can be fed into the steerable catheter. Theproximal tips of the pull wires 12 p and 13 p are fixed to the steeringlever 6 at joints 22 and 23, through any convenient means. In order toprovide a mechanism to hold the lever and pull wires in a chosenposition, to maintain an arcuate configuration of the deflectablesegment, the lever is also rotationally fixed to the round disc 24,which turns in tandem with the pull wire joints 22 and 23, and a brake 7comprising a cam plate 26 and lever 27 is disposed on the handle suchthat the rotation of the brake lever rotates cam plate into interferingcontact with the disc and prevents the disc from rotating. The brakelever and cam plate are held in position by friction between the leverand cam and the fittings use to connect them to the housing. This isshown in FIG. 6, in which the steering lever has been rotated about itsfulcrum 28 (with each pull wire fixed to the lever on opposite sides ofthe fulcrum) to pull the pull wire 12 proximally, while relievingtension and allowing pull wire 13 to translate distally, and the brakinglever has been rotated to jam the cam plate into interfering contactwith the disc to hold it in place. Though this braking system isparticularly suited for use with the pull wire system of FIGS. 1 through5, the advantages of the braking system can be obtained with other pullwire systems, and the advantages of the pull wire system can be usedwith other braking systems. A hemostatic valve 29 is provided at theproximal end of the feeder tube 21.

The inner and outer tube may comprise PEBAX® 7033 SA01 MED WITH FOSTERPropell, or ProPell™ thermoplastic polyurethane (TPU) for the innertube. The liner, when used, may comprise PTFE. The braids may comprisestainless steel braids of between 25 and 100 picks per inch, or the morepreferable pick counts expressed above. The braids are preferably madeof flat wire about 0.007″ wide by 0.001″ thick in a 5.5 French internaldiameter configuration and may be larger in larger configurations andsmaller in smaller configurations. The braid of the deflectable segmentis preferably embedded in a low durometer polymer such as Pebax at 30Dto 35D. The braid of the wound segment is preferably embedded in a highdurometer polymer such as Pebax at about 72D. The braid of thedeflectable segment can be annealed to increase its flexibility, by, forexample, heating the stainless steel braid at high temperature (about1100° F., or 600° C.) for about two minutes. The pull wires arepreferably stainless steel round pull wires with a diameter of about0.006″ or flat pull wires about 0.010″ wide by 0.003″ thick covered in aPTFE liner with a wall thickness of about 0.001″. The pull wires mayalso comprise a stainless steel braid, or a para-aramid synthetic fiber(Kevlar®) tension element. The resultant overall wall thickness for asteerable catheter with a 5.5 F internal diameter, in the deflectablesegment and wound segment, may be about 0.3 to 0.4 mm, preferably about0.367 mm (about 1.1 F). The resultant overall wall thickness for asteerable catheter with an 11 F internal diameter, in the deflectablesegment and wound segment, may be about 0.6 to 0.8 mm, preferably about0.734 mm (about 2.2 F). In such larger diameter cross sections andwalls, larger cross sectional area for pull wires and for braid wirematerial may be used. (Likewise in smaller diameter devices than the 5.5French internal diameter configuration disclosed these cross sectionalareas could be smaller.) These parameters may be varied to adjust thetorque transmission, pushability and trackability of steerable cathetersfor particular applications. Suggested overall dimensions of thesteerable catheters for particular applications are as follows:

Clinical Applications/ Proximal Wound Defl. Target Site Segment segmentSegment ID Femoral vein access across 55 cm 10 cm 5 cm 8.5F the atrialseptum access of the left atrium for AF ablation Femoral vein accessacross 55 cm 10 cm 5 cm 8.5F, the atrial septum to the 10.5F left atriumfor mitral 12.5F valve repair 14.5 F Femoral artery access 80 cm 15 cm 5cm 3.5F across the aortic arch for 4.5F left ventricular 5.5 Fprocedures from femoral access for transendocardial biotherapeuticintervention and coronary artery intervention and peri-valvular leak,Femoral artery access 80 cm 15 cm 5 cm 12F across the aortic arch for14F left ventricular 16F procedures from femoral 18F access 20F foraortic valve implantation Radial artery access to 50 cm 15 cm 40 cm 4.5F the peripheral vasculature 5.5 F of the aorto ostial region forperipheral interventions Radial artery access to 50 cm 20 cm 70 cm 4.5 Fthe peripheral vasculature 5.5 F superior femoral artery for peripheralinterventions Radial artery access to 50 cm 20 cm 10 cm 3.5F the Aorticarch cardiac 4.5F interventions such as 5.5F peri-valvular leak,transendocardial delivery Carotid access 80 cm 15 cm 5 cm 3.5F 4.5F 5.5F

Given these dimensions and the typical size and anatomy of patients, thesteerable catheter components are arranged along the length of thesteerable catheter such that the wound segments coincide with theexpected bend in the vasculature on along predetermined access routes.Generally, the steerable catheter is constructions with dimensions forthe deflectable segment and the wound segment such that, when insertedthrough a predetermined access point, with the deflectable segmentdisposed at a target site, the wound segment is disposed within curvedportion of the vasculature. Depending on the target site, the curvedportion may be the aortic arch, the transition from the inferior venacava to the atrial septum, the iliac bifurcation (for access from oniliac artery to its contralateral iliac artery), the brachiocephalictrunk or the aorta of the patient artery or the aortic arch (fortrans-radial access to the renal arteries), or other tortuosity that maybe encountered between the entry point and the target site. For example,for access to the left atrium of a patient, from the femoral vein, thecurve of the right atrium is expected be located about 55 to 65 cm fromthe entry point into the vasculature (a cut-down in the thigh of thepatient). Thus the steerable catheter for access to the atrial septumfrom the femoral vein is constructed such that, when the inserted in thevasculature, with the deflectable segment disposed within the rightatrium, proximate the atrial septum of the patient (where deflectionfacilitates crossing into the left atrium of the patient), the woundsegment is disposed, in curved configuration, across the right atrium.This can be accomplished, as indicated in the table above, with asteerable catheter having a 5 cm deflectable segment at the distal andof the steerable catheter, followed by a 10 cm wound segment, followedby a proximal segment of at least 55 cm (the proximal segment lengthsdescribed in the table may be considered minimum lengths). Thisrelationship between the steerable catheter structure and thevasculature of a patient is shown in FIG. 7, which illustrate thesteerable catheter 1 used access portions of the heart 30, with thesteerable catheter disposed within the vasculature of a patient, in thepathway leading from the femoral vein, up the inferior vena cava 31,through the right atrium 32, through the atrial septum 33 an into theleft atrium 34, such that the deflectable segment 2 d is disposedproximate the target site of the left atrium and the wound segment 2 wis disposed, in a curved configuration, along around the curve leadingfrom the vena cava to the atrial septum. The proximal segment 2 pextends downs the inferior vena cava to the entry point in the femoralvein. In use, the steerable catheter is inserted into the vasculature,navigated through the vasculature until the deflectable segment of thesteerable catheter is disposed proximate the target site, and, with aproperly sized steerable catheter, the wound segment is disposed acrossa curve in the vasculature. Once properly placed, the deflectablesegment can be deflected by operation of one or more pull wires(tensioning or releasing tension), through manipulation of the steeringmechanism on the proximal handle. During manipulations of the pull wiresand deflection of the deflectable segment, the wound segment, by virtueof the wound nature of the pull wires, will experiencedcircumferentially balances forces and be much less likely to change itsconfiguration or experience whipping common in other steerablecatheters. The method can be used to access many target sites, includingeach of the target sites listed in the table, through correspondinginsertion sites.

Though the steerable catheter has been described in relation to guidecatheters, guide sheaths and introducer sheaths, the inventive aspectsof the steering mechanisms can be adapted to any catheter. Thus, whilethe preferred embodiments of the devices and methods have been describedin reference to the environment in which they were developed, they aremerely illustrative of the principles of the inventions. The elements ofthe various embodiments may be incorporated into each of the otherspecies to obtain the benefits of those elements in combination withsuch other species, and the various beneficial features may be employedin embodiments alone or in combination with each other. Otherembodiments and configurations may be devised without departing from thespirit of the inventions and the scope of the appended claims.

We claim:
 1. A steerable catheter comprising: a tube (2) having aproximal end (4), a distal end (5), and a lumen extending therebetween,said tube (2) having a first segment (2 d) proximate said distal end andsecond segment (2 w) that extends proximally from said first segment (2d) toward said proximal end, a first pull wire (12) disposed within afirst side lumen of the tube (2) and a second pull wire (13) disposedwithin a second side lumen of the tube (2), and extending from thedistal end (5) to the proximal end (4) of the tube (2), said first andsecond pull wires comprising first and second wound segments (12 w, 13w) which are wound about a longitudinal axis of the tube in the secondsegment (2 w) of the tube, with the first wound segment (12 w) and thesecond wound segment (13 w) dispersed circumferentially about thelongitudinal axis of the tube (2); wherein the wound segments (12 w, 13w) are configured to reduce whipping when the tube (2) is rotated aroundthe longitudinal axis of the tube (2); wherein the first pull wire (12)extends distally within the first segment (12 d) of the tube (2) fromthe first wound segment (12 w) in a straight distal segment of the firstpull wire (12 d) and the second pull wire (13) extends distally withinthe first segment (12 d) of the tube (2) from the second wound segment(13 w), in a straight distal segment of the second pull wire (13 d), andsaid straight distal segment of the first pull wire (12 d) and saidstraight distal segment of the second pull wire (13 d) extend distallyon opposite sides of the tube (2), a handle (3) fixed to the tube (2),said handle comprising: means for selectively tensioning the first pullwire without tensioning the second pull wire, or tensioning the secondpull wire without tensioning the first pull wire, to providebidirectional steering of the deflectable segment.
 2. The steerablecatheter of claim 1, wherein: the first pull wire (12) is wound in afirst direction and the second pull wire (13) is wound in the firstdirection, substantially in parallel with the first pull wire.
 3. Thesteerable catheter of claim 1, wherein: the first pull wire and secondpull-wire are counter-wound.
 4. The steerable catheter of claim 1,wherein: the first pull wire (12) extends proximally from the firstwound segment (12 w) in a straight proximal segment of the first pullwire (12 p)and the second pull wire (13) extends proximally from thesecond wound segment (13 w), in a straight proximal segment of thesecond pull wire (13 p), and said straight proximal segment of the firstpull wire (12 p) and said straight proximal segment of the second pullwire (13 p) extend proximally on opposite side of the tube (2).
 5. Thesteerable catheter of claim 1, 2, 3 or 4, wherein: in the first segment(2 d) of the tube, a wall of the tube consists of an inner tube (11),the first pull wire (12) disposed within the first side lumen of thetube (2) and the second pull wire (13) disposed within the second sidelumen of the tube (2), a braid (14) embedded in a low durometer polymerdisposed about the inner tube (11) and pull wires (12 d, 13 d), and anouter tube (10) disposed about the braid (14).
 6. The steerable catheterof claim 5, wherein: in the second segment (2 w) of the tube, the wallof the tube consists of an inner tube (11), the wound segments (12 w, 13w) of the pull wires, the braid (14) embedded in a low durometer polymerdisposed about the inner tube and pull wires, an additional braid (16)disposed about the braid (14), and the outer tube (10) disposed aboutthe additional braid (16).
 7. The steerable catheter of claim 1 or 4,wherein: in the first segment of the tube, the wall of the tube consistsof a liner (15), an inner tube (11) disposed about the liner, the firstpull wire (12) disposed within the first side lumen of the tube (2) andthe second pull wire (13) disposed within the second side lumen of thetube (2), a braid (14) embedded in a low durometer polymer disposedabout the inner tube and pull wires, and an outer tube (10) disposedabout the braid (14).
 8. The steerable catheter of claim 1 or 4,wherein: in the second segment of the tube, the wall of the tubeconsists of a liner (15), an inner tube (11) disposed about the liner(15), the wound segments (12 w, 13 w) of the pull wires disposed aboutthe inner tube (11), a braid (14) embedded in a low durometer polymerdisposed about the inner tube and pull wires, and an outer tube (10)disposed about the braid (14).
 9. The steerable catheter of claim 1,wherein: the first and second wound segments (12 w, 13 w) each comprisethree turns about the longitudinal axis of the tube.
 10. The steerablecatheter of claim 1, further comprising a handle (3) fixed to the tube(2), said handle comprising: a steering lever (6) rotatably secured tothe handle at a fulcrum (28), with the first and second pull wires (12,13) fixed to the steering lever (6) on opposite sides of the fulcrum(28); a disc (24) rotationally fixed to the steering lever (6); and abrake (7) disposed on the handle such that the rotation of the brakeprevents rotation of the disc (24), thereby holding the first segment ofthe tube (2 d) in a configuration corresponding to the rotationalposition of the steering lever (6).
 11. The steerable catheter of claim10, wherein the brake comprises: a brake lever (27) and a cam plate(26), disposed on the housing, such that the rotation of the brake lever(27) rotates the cam plate (26) into interfering contact with the disc(24) and prevents the disc (24) from rotating.
 12. The steerablecatheter of claim 1, wherein: the wound segments (12 w, 13 w) areconfigured to minimize changes in curve geometry when the tube (2) isrotated around a long axis of the tube (2) while constrained within acurve.
 13. The steerable catheter of claim 1, wherein: the woundsegments (12 w, 13 w) configured to reduce whipping when the tube (2) isrotated around a long axis of the tube (2) while constrained within acurve of a vessel with a patient's body.
 14. The steerable catheter ofclaim 1, wherein: the wound segments (12 w, 13 w) configured to reducewhipping when the tube (2) is rotated around a long axis of the tube (2)while the second segment (2 w) is constrained within a curve of a vesselwith a patient's body.
 15. The steerable catheter of claim 1, wherein:the wound segments (12 w, 13 w) configured to minimize changes in curvegeometry when the tube (2) is deployed within a vessel of a patient. 16.The steerable catheter of claim 1, wherein: the wound segments (12 w, 13w) configured to minimize changes in curve geometry when the tube (2) isdeployed within a vessel of a patient, such that the wound segment (2 w)is disposed in a bend in the vessel.
 17. The steerable catheter of claim1 or 4, wherein: said first and second pull wires comprise first andsecond straight distally extending segments (12 d, 13 d) extendingdistally from the respective wound segments (12 w, 13 w); and the firstand second straight distally extending segments (12 d, 13 d) aredisposed within the first segment (2 d) of the tube; and the first andsecond wound segments (12 w, 13 w) are disposed in the second segment ofthe tube.
 18. The steerable catheter of claim 1, wherein the means forselectively tensioning comprises: a steering lever (6) rotatably securedto the handle at a fulcrum (28), with the first and second pull wires(12, 13) fixed to the steering lever (6) on opposite sides of thefulcrum (28).
 19. The steerable catheter of claim 18, furthercomprising: a disc (24) rotationally fixed to the steering lever (6); abrake (7) disposed on the handle such that the rotation of the brakeprevents rotation of the disc (24), thereby holding the first segment ofthe tube (2 d) in a configuration corresponding to the rotationalposition of the steering lever (6).
 20. A method of accessing a targetsite in a vessel of a patient, said method comprising the steps of:providing a steerable catheter comprising: a tube (2) having a proximalend (4), a distal end (5), and a lumen extending therebetween, said tube(2) having a first segment (2 d) proximate said distal end and secondsegment (2 w) that extends proximally from said first segment (2 d)toward said proximal end, a first pull wire (12) disposed within a firstside lumen of the tube (2) and a second pull wire (13) disposed within asecond side lumen of the tube (2), and extending from the distal end (5)to the proximal end (4) of the tube (2), said first and second pullwires comprising first and second wound segments (12 w, 13 w) which arewound about a longitudinal axis of the tube in the second segment (2 w)of the tube, with the first wound segment (12 w) and the second woundsegment (13 w) dispersed circumferentially about the longitudinal axisof the tube (2); wherein the wound segments (12 w, 13 w) are configuredto reduce whipping when the tube (2) is rotated around the longitudinalaxis of the tube (2), a handle (3) fixed to the tube (2), said handlecomprising: means for selectively tensioning the first pull wire withouttensioning the second pull wire, or tensioning the second pull wirewithout tensioning the first pull wire, to provide bidirectionalsteering of the deflectable segment; inserting the steerable catheterinto a vessel of the patient, and navigating the steerable catheterthrough the vessel of the patient until the first segment of the tube isdisposed proximate the target site and the second segment is disposedacross a curve in the vessel; and operating one or both of the pullwires to deflect the first segment of the tube; and rotating the tubeabout the long axis of the tube (2) while the steerable catheter isdisposed within the vessel.
 21. The method of claim 20, wherein: thefirst pull wire (12) is wound in a first direction and the second pullwire (13) is wound in the first direction, substantially in parallelwith the first pull wire.
 22. The method of claim 20, wherein: the firstpull wire and second pull-wire are counter-wound.
 23. The method ofclaim 20, wherein: the first pull wire (12) extends proximally from thefirst wound segment (12 w) in a straight proximal segment of the firstpull wire (12 p) and the second pull wire (13) extends proximally fromthe second wound segment (13 w), in a straight proximal segment of thesecond pull wire (13 p), and said straight proximal segment of the firstpull wire (12 p) and said straight proximal segment of the second pullwire (13 p) extend proximally on opposite side of the tube (2).
 24. Themethod of claim 20, wherein the steerable catheter comprises at leasttwo pull wires, and the wound segments are dispersed about thecircumference of the steerable catheter.
 25. The method of claim 20,wherein the target site is a left atrium and the curve is a transitionfrom an inferior vena cava to an atrial septum of the patient.
 26. Themethod of claim 20, wherein the target site is an iliac artery of apatient and the curve is an iliac bifurcation of the patient.
 27. Themethod of claim 20, wherein the target site is a left ventricle of apatient and the curve is an aortic arch of the patient.
 28. The methodof claim 20, wherein the target site is a coronary artery of a patientand the curve is an aortic arch of the patient.
 29. The method of claim20, wherein the target site is an aortic valve of a patient and thecurve is an aortic arch of the patient.
 30. The method of claim 20,wherein the target site is a peripheral blood vessel of a patient andthe curve is a tortuosity between the target site and an entry pointinto the vasculature of the patient.
 31. The method of claim 20, whereinthe target site is a carotid artery of a patient and the curve is abifurcation of the brachiocephalic trunk or the aorta of the patient.32. The method of claim 20, wherein the steerable catheter is furthercharacterized in that: the first pull wire (12) extends distally withinthe first segment (2 d) of the tube (2) from the first wound segment (12w) in a straight distal segment of the first pull wire (12 d) and thesecond pull wire (13) extends distally within the first segment (2 d) ofthe tube (2) from the second wound segment (13 w), in a straight distalsegment of the second pull wire (13 d), and said straight distal segmentof the first pull wire (12 d) and said straight distal segment of thesecond pull wire (13 d) extend distally on opposite sides of the tube(2).